The present invention relates to an apparatus and a method having or using a movable section, a fixed section, an elastic member for connecting the movable section with the fixed section, magnetic field generating means, a drive coil, a detection coil and others, and more particularly to an apparatus and a method for driving an actuator by which the movable section is constantly vibrated in the resonance state.
Heretofore, as an example of an electromagnetic actuator, there has been, for example, an actuator used in an optical pickup. This is used for performing tracking control with a vibrating mirror. In this actuator, both a mirror drive coil and a mirror vibration detection coil are provided on the movable section, and a magnet is provided on the fixed section. When an electric current is applied to the actuator drive coil, the mirror is driven by a Lorentz force. At this time, the induced electromotive force prosectional to a speed is generated in order that the detection coil makes a movement in the magnetic field. This induced electromotive force serves as a vibration detection signal.
The structure in which two kinds of coils are fixed at positions close to each other and arranged in the movable section in this manner will be considered. In this structure, an electromotive force is generated to the vibration detection coil besides the induced electromotive force prosectional to a speed. This is the electromotive force caused due to the mutual induction action of both the coils when a change in the electric current applied to the drive coil occurs.
Here, FIG. 1 shows a frequency response characteristic of a sensor (angular velocity) signal relative to a drive signal. A horizontal axis represents a frequency. In this example, the logarithm is shown. An amplitude of the sensor signal is also shown in terms of the logarithm (dB).
When a frequency of the drive signal becomes a specific frequency (resonant frequency), an amplitude of the sensor signal becomes maximum. At this time, a deflection angle also becomes maximum.
Meanwhile, the frequency response characteristic shown in FIG. 1 shows an ideal state. However, since the drive coil and the detection coil are actually contiguous with each other, the signal caused due to mutual induction of both the coils is disadvantageously included in the sensor signal.
That is, the magnetic field whose direction is substantially vertical to the mirror plane is generated in the drive coil when it is assumed that the electric current flowing to the drive coil is determined as follows:I=I0 sin ωt  (1)
Since it can be considered that the magnetic flux density of that magnetic field is substantially prosectional to the electric current, it is possible to determine as follows:B=KI=KI0 sin ωt=B0 sin ωt  (2)
(K=Proportional Number)
On the other hand, the magnetic filed represented by the expression (2) is generated in the detection coil. Further, the induced electromotive force is produced by the electromagnetic induction in order to realize changes with time. Assuming that the magnetic field in the detection coil is approximately uniform at the value of the expression (2) and an internal area of the detection coil is A, the generated electromotive force is expressed as follows:V=−(dBA/dt)=−ωB0A cos ωt  (3)
Since the signal obtained by the mutual induction action is a signal irrespective of the vibration, it is not desirable that this signal is included in the vibration detection signal.
In light of the above-described point, Japanese Patent Application KOKAI Publication No. 64-2015 discloses a technique concerning a vibration mirror apparatus. This apparatus provides a third coil to the fixed section and negatively feeds back the electromotive force output caused due to the mutual induction action of the drive coil and the third coil to an output of the vibration detection coil. As a result, only the induced electromotive force prosectional to a speed is detected.
Furthermore, Japanese Patent Application KOKOKU Publication No. 7-70083 discloses a technique concerning the vibration mirror apparatus. In this apparatus, the drive coil is arranged inside a closed magnetic circuit and the detection coil is arranged outside the closed magnetic circuit, respectively. Decreasing the mutual induction action between both the coils generates only the induced electromotive force prosectional to a substantial speed in the detection coil.
However, in the technique disclosed in Japanese Patent Application KOKAI Publication No. 64-2015, since a coil must be newly provided to the fixed section, the structure becomes complicated, which may be an obstacle for reduction in cost and size. Moreover, a positions of the detection coil and the third coil relative to the drive coil are different from each other in a narrow sense, and the mutually-induced electromotive force differs. Thus, the unnecessary signal component can not be completely removed.
In addition, in the technique disclosed in Japanese Patent Application KOKOKU Publication No. 7-70083, the magnetic shield effect of the closed magnetic circuit is utilized, but this is not perfect. Therefore, the mutually-inductive electromotive force of the drive coil and the detection coil can not be completely removed. Additionally, it is most effective to arrange both the coils at positions far from an oscillating axis by nature, whereas the magnetic circuit must be arranged between both the coils in this conventional technique. Accordingly, optimization of the coil positions is difficult.